LITERATURA CITADA

Results of the current study revealed that fundamental frequency but not formant dispersion was related to age; younger (but post-pubertal) males had lower fundamental frequency. In line with the prediction, this study found a significant negative relationship between the fundamental frequency of the male voice and various measures of body shape including shoulder and chest circumferences and Shoulder-Hip Ratio. Lower fundamental frequencies indicated individuals with a larger body shape, specifically in terms of upper body musculature. Fundamental frequency was also related to one measure of body size; weight was significantly negatively correlated with fundamental frequency. Further, a stronger significant negative relationship was also found between formant dispersion and body size (weight and height). Interestingly, a relationship was also found between formant dispersion and body shape (neck, shoulder, chest and waist circumferences and Shoulder Hip Ratio). Smaller formant dispersion indicated males with a larger body size and shape.

First, with regard to body shape and fundamental frequency, findings of a relationship between low fundamental frequency and large body shape, a large upper musculature, suggests that a speaker‟s fundamental frequency

provides a cue to body configuration. Low fundamental frequency and sexually dimorphic body configuration are both determined at puberty by the action of testosterone and may therefore be honest multi-channel signals of genetic quality and hormonal health to female mates.

Second, with regard to formant frequency and body size, Gonzalez (2004) found a weak relationship between formant frequencies and height and weight and Sachs et al. (1972) found a negative correlation between vowel formant frequencies and height. The current study supports these findings although the correlation between formant frequencies was stronger for weight than height.

Both Gonzalez (2004), and the current study, found a weaker relationship between body size and formant frequencies in humans than Fitch (1997) found in rhesus macaques. One possible explanation of a weaker relationship between formant frequency and body size in humans than other primates is that the secondary descent of the larynx in human males disassociates vocal tract length from skeletal and body size (Fitch, 1997). Indeed, Gonzalez (2004) found a stronger relationship between formant frequencies and body size in women than males, supporting this proposal.

Thirdly, the current study also found a correlation between formant dispersion and body shape not previously reported. Body shape or SHR and

fundamental frequency are known to be largely dependant on levels of testosterone present at puberty. The control mechanism by which the larynx

is lowered in human males is currently unknown, however these results imply that testosterone may also play a role here although it is most likely that these changes in the larynx are under the influence of an interaction between both sex and growth hormones as suggested by Fitch (1997).

Finally, once the age of participant was controlled for, the current study involving English speaking males found a correlation between fundamental frequency and weight not previously reported. However, the relationship between weight and formant dispersion and fundamental frequency must be viewed with caution, since the prevalence of overweight individuals in Western society may weaken any correlation (Fitch, 1999).

Examination of the graph displaying the relationship between age and fundamental frequency (Figure 2a) suggests that there may have been

outliers in the data set. Whilst an outlier analysis could have been performed, there was no valid reason to exclude data on the grounds that there were no particularly unusual values for any variable given the wide age range of the participants.

Chapter Summary

To attempt to understand how aspects of the human male voice may be involved in courtship and competitive behaviours in humans the first study of this thesis investigated whether these acoustic parameters

were related to both physical measures and age in human males. Results suggested that relationships between physical and acoustic parameters in human males do exist. Fundamental frequency was found to be related to age, and both fundamental and formant frequencies were related to aspects of both body size and shape. It is therefore plausible that the human male voice provides an acoustic signal of such attributes to potential female mates and male rivals. The question of why such acoustic cues would be necessary when in most (although not all) situations the listener is probably able to see the speaker is addressed later in this thesis.

CHAPTER 3

Is the voice an honest signal of hormonal quality?

Note: Aspects of this chapter have been published in Evans, S., Neave, N., Wakelin,

D. and Hamilton, C. (2008). The relationship between testosterone and vocal frequencies in human males. Physiology & Behavior. 93, 783-788.

The previous study demonstrated that aspects of the human male voice are related to age and various measures of body shape and size but do fundamental and formant frequencies also reflect hormonal status? It is thought that sexual dimorphism of the male voice which primarily occurs during puberty is (in part at least) under the influence of the sex steroid hormone testosterone. There is also some evidence that vocal parameters remain correlated with circulating levels of testosterone in adulthood suggesting that the voice may provide an honest signal of hormonal quality. Thus the second study in this thesis seeks to further investigate this relationship, and also examines the putative relationship between prenatal testosterone (as measured by 2D:4D ratio) and male vocal parameters. In addition, any relationship between salivary cortisol and male vocal frequencies are also explored.